The bug

When using the /tp command with integer values, the entity being teleported will be centred to y+=0.5 in addition to being centred on the x and z axes.

How to reproduce

1. Create a new world
2. Go into spectator mode
3. Run /tp @s 0 0 0

If you look at the block coordinates, you will end up at x=0.5 and z=0.5, as expected. But you will also end up at y=0.5.